Demonstration of Optical 56Gbps NRZ for 400GbE PMD...

HUAWEI TECHNOLOGIES CO., LTD.

Demonstration of Optical 56Gbps NRZ

for 400GbE PMD Using 56Gbps SerDes

IEEE802.3bs 400GbE Task Force

San Antonio Plenary Meeting

November, 2014

Yangjing Wen, Fei Zhu, and Yusheng Bai

Huawei Technologies, US R&D Center

and

Haoli Qian and Jeff Twombly

Credo Semiconductor


Contents

Introduction

Experimental setup

Eye diagrams

BER and receiver sensitivity

Optical link budget estimation

Summary


Supporters

- Mizuki Shirao, Mitsubishi Electric Corporation

- Keisuke Kojima, Mitsubishi Electric Corporation


Introduction

56Gb/s NRZ considered a promising candidate for 400GbE PMD due to its

simplicity, high sensitivity, and high tolerance to MPI:

cole_01_0914_smf.pdf; qian_3bs_01_0714.pdf; zhu_3bs_01a_0514.pdf;

zhu_3bs_01_0714.pdf; shirao_3bs_01a_0714.pdf; stassar_01_1014_smf.pdf

In September Interim Meeting, we demonstrated optical 56Gbps NRZ

operation using commercially available 43G optical transmitter and receiver

for 400GbE PMD (wen_3bs_01_0914.pdf).

The electrical signal in wen_3bs_01_0914.pdf was generated by using

56Gbps bit pattern generator, which is an instrument. There has been concern

regarding the availability of 50GHz electrical I/O.

It is desirable to demonstrate 56Gbps electrical signaling generation using

SerDes, which is important for practical implementation.


Work in this Presentation

In this presentation, we

- Demonstrate 56Gbps NRZ for 400GbE PMD using 56Gbps

SerDes electrical signaling with commercial 43Gbps optical

components

- Evaluate receiver sensitivity for both BtB and with chromatic

dispersion

- Analyze optical link budget for 400GbE 2km and 10km PMD


Experimental Setup

PIN+TIA

PM

VOA

U2t 3dB BW: 35GHz

55Gbps

(prbs15)

Mitsubishi, 1535 nm

3dB BW: 35GHz

DSO Offline

DSP

Credo Eva

Board

Clk Agilent 40G

optical module

SerDes

Driver

+ EML

synthe

sizer

Agilent

80GS/s DSO

DCA

OSA

Operation conditions of driver and EML:

- Laser bias current = 80mA

- Operating temperature: 40 deg C

- VOS =-2.0V; VEE=-5.2V;

VG=-2.2V; VX =-1.5V

Tx analog equalizer: 3-tap FFE

Rx equalizer: 5-tap FFE

Equalization algorithm:

- LMS with no training

S21 responses of Mitsubishi driver+EML and U2t

receiver can be found in wen_3bs_01_0914.pdf


Credo 56G SerDes

Based on commercially available 40nm CMOS technologies

Using analog equalization in TX

55Gbps 50Gbps

Eye Diagrams of SerDes Output


Optical Eye Diagrams

With Credo SerDes, 55Gbps With SHF BPG, 56Gbps

ER = 9.6dB

The optical eye diagram using Credo SerDes has similar eye

quality to that of using a bit pattern generator (instrument)


BER vs Average Optical Power

1535nm

The BtB sensitivity is around -16.7dBm at BER@1e-3 and -15.8dBm at BER@2e-4

Negative dispersion experiences negative penalty due to positive chirping

Observed dispersion penalty due to positive dispersion is less than 0.5dB

Dispersion used in test covers the

worst cases for both wavebands of:

1286.66~ 1318.35 nm

And

1295.56~ 1327.69 nm

-17.5 -17 -16.5 -16 -15.5 -15 -14.5 -1410

-6

10-5

10-4

10-3

10-2

Average Optical Power (dBm)

BE

R

BtB

19.1 ps/nm dispersion

-28.5 ps/nm dispersion


Dispersion Effect for Different Wavelengths

Dispersion (DL) at

1535 nm

Operating wavelength

at 1310nm window

For the same dispersion effect, Equivalent

dispersion at operating wavelength

19.1 ps/nm 1328.78 nm 25.5 ps/nm

19.1 ps/nm 1319.42 nm 25.9 ps/nm

-28.5 ps/nm 1285.65 nm -40.6 ps/nm

Dispersion effect applied on optical signal via L2

DLc

L

2

2

2

2 – 2nd order derivative of propagation constant over frequency

L – fiber length

D – fiber dispersion coefficient

– wavelength

c – speed of light

The same dispersion amount has different dispersion effect at different wavelengths


Comparison Between Credo SerDes and SFH BPG

1535nm

Back-to-back

Credo SerDes and SHF BPG have similar BtB performance

This offline result using BPG has about 1.8dB sensitivity improvement at BER@1e-3

compared with that in wen_3bs_01_0914.pdf (also see next page), which may be due to:

- The offline result has an FFE equalizer

- The result in wen_3bs_01_0914.pdf had no CDR and may have suffered more jitter

-17.5 -17 -16.5 -16 -15.5 -15 -14.5 -1410

-6

10-5

10-4

10-3

10-2

Average Optical Power (dBm)

BE

R

Credo SerDes

SHF BPG


Comparison Between prbs31 and prbs15

Offline processing difficult to go to high

order prbs

Concern being addressed that prbs15 is

too short for PAM4

We compare prbs31 and prbs15 for NRZ

using:

- SHF BPG: for bit pattern generation

- SHF BER analyzer: for real time BER test

- Mitsubishi EML: transmitter

- U2t Receiver

- No CDR used

No difference observed in BER performance between prbs31 and

prbs15 for NRZ

-16 -15.5 -15 -14.5 -14 -13.5 -13 -12.5 -12 -11.5 -1110

-7

10-6

10-5

10-4

10-3

10-2

Average Optical Power(dBm)

BE

R

prbs15

prbs31


Link Budget in OMA

Applications Duplex 2km Duplex 10km

Number of wavelength 8

Baud rate 53.2 GBaud/s 56 GBaud/s

Operating BER 2e-4 1e-3

ER ≥6dB

Transmitter output OMA (1) 2.0dBm 3.3dBm

Mux IL(2) 3dB 3dB

Fiber/connector loss(3) 5dB 6.4dB

MPI penalty (4) 0.2dB 0.2dB

Dispersion penalty (1) 1.0dB 1.5dB

DeMux IL(2) 3dB 3dB

Post-DeMux Rx input OMA -10.2dBm -10.8dBm

Rx sensitivity (OMA)(5) -12.6dBm -13.3dBm

Margin 2.4dB 2.5dB

(1) shirao_3bs_01_0914.pdf, preliminary specifications

(2) cole_01_0914_smf.pdf ; (3) kolesar_3bs_01_0514.pdf; (4) wen_3bs_01_0914.pdf

(5) The receiver sensitivity was measured in average power at 55Gbps with ER=9.6dB, and

has been converted to OMA with ER=6dB for 56Gpbs and 53.2Gbps respectively


Summary

Demonstrated the feasibility of 8x56G NRZ for

400GbE 2km and 10km PMD using 56G SerDes

electrical signaling

There is sufficient link budget for both 2km and

10km (with 2.5dB margin) applications

Demonstration of Optical 56Gbps NRZ for 400GbE PMD...

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